1. Field of the Invention
This invention relates generally to the field of computer network security protocols. More particularly, the invention provides an enhanced transport layer security (“ETLS”) protocol that is especially well-suited for use with mobile communication devices, such as Personal Digital Assistants, cellular telephones, and wireless two-way e-mail communication devices (collectively referred to hereinafter as “mobile devices”).
2. Description of the Related Art
Security protocols for establishing a secure connection to a computer network, such as the Internet, are known. A security protocol commonly used to securely connect to an Internet host is the Transport Layer Security (“TLS”) protocol, which was formerly known as the Secure Socket Layer (“SSL”) protocol.
FIG. 1 is a signal flow diagram 10 illustrating the basic steps typically used to establish a secure connection between a client 12 and an Internet server 14 using the TLS protocol. In step 16, an initial datagram is transmitted from the client 12 to the server 14 to establish contact and to identify the algorithms or languages that the client 12 is capable of supporting. Once the initial datagram is received, the server 14 typically accepts the connection and replies with a datagram that identifies the algorithms or languages that the server will support (step 18). In addition, the reply datagram from the server 14 typically includes a public key in a digital certificate that authenticates the identity of the server 14. The digital certificate is generally acquired from a trusted third-party, such as VeriSign™ or some other certificate authority, which verifies that the public key belongs to the server 14. In addition, the public key typically has an associated private key that is maintained only by the server 14, whereby data encrypted with the public key can only be decrypted using the private key.
In steps 20 and 22, the client 12 negotiates a session key with the server 14. The session key is typically a random number generated by the client 12 that is used for only one fetch-response operation between the client 12 and server 14. The random session key is typically first used to encrypt some random data as “proof of the key.” The session key and the data are then encrypted with the public key and transmitted to the server in step 20. The session key and “proof of key” data are decrypted by the server using its private key. The “proof of key” data is then further decrypted with the session key. Then, in step 22, the server typically transmits the “proof of key” data back to the client 12 to establish that it has properly received and decrypted the session key.
Once the TLS public key has been exchanged and a session key has been negotiated, a secure TLS socket is established, and application data may be securely transmitted between the client 12 and server 14 using the session key (step 24). By utilizing this four-pass handshake between a client and a server each time a communication is initiated, the TLS protocol ensures both the authenticity of the server and the originality of the transmission. For example, to illustrate the importance of originality, if a user has communicated with a bank server via a client to electronically transfer money from an account, the four-pass TLS handshake prevents the transfer operation from being repeated by “replaying” the same encrypted message from either the same client or another client if the communication was intercepted.
Although the TLS protocol provides a secure connection to a server, this protocol is not well-suited for mobile applications because the datagrams transferred in the TLS four-pass handshake typically contain a relatively large amount of data that cannot be quickly transferred over a wireless network. Therefore, in order to reduce the number of datagrams transferred over the wireless network, mobile applications commonly utilize a Wireless Application Protocol (“WAP”) to establish a secure connection with an Internet server.
FIG. 2 is a block diagram illustrating a typical mobile communication system 30 utilizing the Wireless Application Protocol (WAP). In this system 30, a service request from a mobile device 32 that is addressed to a server 34 is encoded using a Wireless Transport Layer Security (WTLS) protocol and transmitted through a wireless gateway 36 to a WAP Gateway 38, which typically acts as a proxy to the Internet. The wireless gateway and WAP gateway may or may not be co-located. Typically, the WAP Gateway 38 has its own digital certificate, signed by a trusted third-party that is used by the mobile device 32 to validate its authenticity. Once the WTLS-encrypted service request is received, the WAP Gateway 38 generally establishes a TLS connection over the Internet with the server 34. The service request is then decrypted by the WAP Gateway 38, re-encrypted using the TLS protocol and sent over the Internet to the server 34. To respond to the service request, the server 34 typically transmits TLS-encrypted data to the WAP Gateway 38, which is then decrypted and re-encrypted using the WTLS protocol and transmitted to the mobile device 32. Although this system 30 is typically faster than the TLS protocol for mobile applications, it leaves a gap in the secure link, thereby risking that data may be intercepted while it is in plaintext format in the WAP Gateway 38.